In a construction machine such as a wheel loader, a so-called negative parking brake that is activated by biasing force of a spring or the like obtained by discharging hydraulic fluid from a brake cylinder is employed (see, for instance, Patent Literature 1). In such a parking brake, the hydraulic fluid is supplied to the brake cylinder through a parking brake hydraulic circuit, thereby releasing the parking brake.
A parking brake hydraulic circuit of a construction machine is occasionally connected to a hydraulic fluid supplying circuit that supplies hydraulic fluid to a transmission so as to be supplied with the hydraulic fluid from the hydraulic fluid supplying circuit. In this arrangement, when the hydraulic fluid is flowed into the transmission in activation (e.g., gear shifting) of the transmission, fluid pressure of the hydraulic fluid supplying circuit may be temporarily decreased. When such decrease in the fluid pressure affects the parking brake hydraulic circuit, the hydraulic fluid is discharged from the brake cylinder to activate the parking brake, so that a brake-dragging phenomenon occurs during travelling.
In order to prevent this phenomenon, a check valve that prevents flowback of the hydraulic fluid toward the hydraulic fluid supplying circuit is provided in the parking brake hydraulic circuit. Even though the fluid pressure of the hydraulic fluid supplying circuit is temporarily decreased in activation (e.g., gear shifting) of the transmission, since the fluid pressure of the parking brake hydraulic circuit is kept at a predetermined value or more by the check valve, the parking brake is maintained in a released state.